CN105633912A - Optical transformer-based internal asymmetric fault protection method for generator - Google Patents

Abstract

The invention discloses an optical transformer-based internal asymmetric fault protection method for a generator. Three-phase currents of a generator terminal side of the generator and three-phase currents of a neutral point side are measured by an optical transformer respectively; a protection device calculates the following parameters: (1) a real part, a virtual part and an effective value of a negative-sequence current of a generator terminal; and (2) the real part, the virtual part and the effective value of the negative-sequence current of a neutral point respectively; and an internal asymmetric fault of the generator is judged and protection acts quickly than tripping when the three conditions are simultaneously met as follows: (1) the negative-sequence current of the generator terminal is greater than a constant value; (2) the negative-sequence current of the neutral point is greater than the constant value; and (3) the rear part of the vector ratio of the negative-sequence current of the generator terminal to the negative-sequence current of the neutral point is smaller than 0. The method has the advantages that (1) the constant value of each negative-sequence current only needs to avoid an unbalanced current during normal operation and the protection has relatively high sensitivity; and (2) a saturation problem does not exist in the optical transformer, the difference in an internal fault and an external fault is relatively obvious and the protection has relatively high sensitivity.

Description

The inner asymmetric fault protecting method of a kind of generator based on optical transformer

Technical field

The invention belongs to field of relay protection in power, in particular to the inner asymmetric fault protecting method of a kind of generator based on optical transformer and corresponding relaying device or monitoring device.

Background technology

At present, internal fault of electric generator mainly adopts longitudinal difference protection and longitudinal zero-sequence over-voltage protection to reflect. Longitudinal difference protection can only reflect phase fault, can not reflect interturn in stator windings fault, and owing to affecting by CT saturation, it is necessary to take faulty action preventing measure; And longitudinal zero-sequence over-voltage protection sensitivity is lower, generally it is difficult to reflection stator branch and snaps fault. The present invention utilizes optical transformer not have the particular advantages of saturation problem, adopts optical transformer to measure generator machine end and neutral point current, utilizes negative phase-sequence electric current to realize the asymmetric fault protection in a kind of highly sensitive inside.

Summary of the invention

The main purpose of the present invention: propose the inner asymmetric fault protecting method of a kind of generator based on optical transformer, it is possible to the inner asymmetric fault of Sensitive Detection generator, owing to not having CT saturation problem, protection has higher reliability.

The technical solution adopted in the present invention is:

Based on the inner asymmetric fault protecting method of generator of optical transformer, utilize optical transformer to measure generator machine end side tri-phase current and neutral point side tri-phase current respectively, and adopt following steps to realize the inner asymmetric fault protection of generator:

Step one: calculate the real part of machine end negative phase-sequence electric current, imaginary part and virtual value by the tri-phase current of machine end side;

Step 2: calculate the real part of neutral point negative phase-sequence electric current, imaginary part and virtual value by the tri-phase current of neutral point side;

Step 3: differentiate following three conditions:

Condition (1): machine end negative phase-sequence electric current virtual value is greater than definite value;

Condition (2): neutral point negative phase-sequence electric current virtual value is greater than definite value;

Condition (3): the real part of the vector ratio of machine end negative phase-sequence electric current and neutral point negative phase-sequence electric current is less than 0;

When three conditions meet simultaneously, being judged in generator district asymmetric fault, protection quick motion is in tripping operation.

Further, the condition in step 3 (3) adopts following formula to calculate:

$\mathrm{Re}\left(\frac{I_{T2.\mathrm{Re}}+{\mathrm{jI}}_{T2.\mathrm{Im}}}{I_{N2.\mathrm{Re}}+{\mathrm{jI}}_{N2.\mathrm{Im}}}\right)<0;$

Wherein, I_T2.Re��I_T2.ImIt is respectively real part, the imaginary part of machine end negative phase-sequence electric current vector; I_N2.Re��I_N2.ImIt is respectively real part, the imaginary part of neutral point negative phase-sequence electric current vector; J is the imaginary unit of vector; Function Re () represents the real part asking for vector in bracket.

The invention has the beneficial effects as follows: can the inner asymmetric fault of Sensitive Detection generator, and there is not CT saturation problem, protection has higher reliability.

Accompanying drawing explanation

Fig. 1 is that in the present invention, generator machine end side tri-phase current and neutral point side tri-phase current measure schematic diagram,

Wherein, CT₁For machine end side three-phase current transformer, CT₂For neutral point side three-phase current transformer, CT₁And CT₂It is optical transformer, after synchronous by merge cells, sampled value is given generator protector, WithIt is respectively machine end tri-phase current,WithIt is respectively neutral point tri-phase current.

Fig. 2 is specific embodiment of the invention step.

Embodiment

Below with reference to accompanying drawing, the technical scheme of the present invention is described in detail.

As shown in Figure 1, Fig. 1 is that in the present invention, generator machine end side tri-phase current and neutral point side tri-phase current measure schematic diagram to specific embodiment, wherein, and CT₁For machine end side three-phase current transformer, CT₂For neutral point side three-phase current transformer, CT₁And CT₂It is optical transformer, after synchronous by merge cells, sampled value is given generator protector,WithIt is respectively machine end tri-phase current,WithIt is respectively neutral point tri-phase current.

Protector utilizes optical transformer to measure generator machine end side tri-phase current and neutral point side tri-phase current respectively, and adopts process step as shown in Figure 2 to realize the inner asymmetric fault protection of generator:

Step one: calculate the real part of machine end negative phase-sequence electric current, imaginary part and virtual value by the tri-phase current of machine end side;

Step 2: calculate the real part of neutral point negative phase-sequence electric current, imaginary part and virtual value by the tri-phase current of neutral point side;

Step 3: differentiate following three conditions:

Condition (1): machine end negative phase-sequence electric current virtual value is greater than definite value, this definite value is normally run unbalanced current by hiding and is adjusted;

Condition (2): neutral point negative phase-sequence electric current virtual value is greater than definite value, this definite value is normally run unbalanced current by hiding and is adjusted;

Condition (3): the real part of the vector ratio of machine end negative phase-sequence electric current and neutral point negative phase-sequence electric current is less than 0.

When three conditions meet simultaneously, being judged in generator district asymmetric fault, protection quick motion is in tripping operation.

As present invention further optimization scheme, the real part of the vector ratio of above-mentioned machine end negative phase-sequence electric current and neutral point negative phase-sequence electric current is less than 0, adopts following formula to calculate:

$\mathrm{Re}\left(\frac{I_{T2.\mathrm{Re}}+{\mathrm{jI}}_{T2.\mathrm{Im}}}{I_{N2.\mathrm{Re}}+{\mathrm{jI}}_{N2.\mathrm{Im}}}\right)<0;$ Formula (1)

Wherein, I_T2.Re��I_T2.ImIt is respectively real part, the imaginary part of machine end negative phase-sequence electric current vector; I_N2.Re��I_N2.ImIt is respectively real part, the imaginary part of neutral point negative phase-sequence electric current vector; J is the imaginary unit of vector; Function Re () represents the real part asking for vector in bracket.

Technical scheme disclosed in this invention can the inner asymmetric fault of Sensitive Detection generator, and there is not CT saturation problem, protection has higher reliability.

Above embodiment is only the technological thought that the present invention is described, can not limit protection scope of the present invention with this, and every technological thought proposed according to the present invention, any change done on technical scheme basis, all falls within protection domain of the present invention.

Claims (2)

1. the inner asymmetric fault protecting method of the generator based on optical transformer; it is characterized in that: utilize optical transformer to measure generator machine end side tri-phase current and neutral point side tri-phase current respectively, and adopt following steps to realize the inner asymmetric fault protection of generator:

Step one: calculate the real part of machine end negative phase-sequence electric current, imaginary part and virtual value by the tri-phase current of machine end side;

Step 2: calculate the real part of neutral point negative phase-sequence electric current, imaginary part and virtual value by the tri-phase current of neutral point side;

Step 3: differentiate following three conditions:

Condition (1): machine end negative phase-sequence electric current virtual value is greater than definite value;

Condition (2): neutral point negative phase-sequence electric current virtual value is greater than definite value;

Condition (3): the real part of the vector ratio of machine end negative phase-sequence electric current and neutral point negative phase-sequence electric current is less than 0;

When three conditions meet simultaneously, being judged in generator district asymmetric fault, protection quick motion is in tripping operation.

2. the inner asymmetric fault protecting method of a kind of generator based on optical transformer as claimed in claim 1, it is characterised in that: the condition (3) in step 3 adopts following formula to calculate:

$\mathrm{Re}\left(\frac{I_{T2.\mathrm{Re}}+{\mathrm{jI}}_{T2.Im}}{I_{N2.\mathrm{Re}}+{\mathrm{jI}}_{N2.Im}}\right)<0;$

Wherein, I_T2.Re��I_T2.ImIt is respectively real part, the imaginary part of machine end negative phase-sequence electric current vector; I_N2.Re��I_N2.ImIt is respectively real part, the imaginary part of neutral point negative phase-sequence electric current vector; J is the imaginary unit of vector; Function Re () represents the real part asking for vector in bracket.